A vehicle oil pump apparatus disclosed in a Japanese Utility Model Application published as No. 1993-96483 is provided with a base portion, a rotor acting as a pump, a drive shaft, and a sealing member. The base portion includes an operating chamber, a shaft aperture, a suction port, a discharging port, a suction passage supplying an oil to the suction port, and a discharged passage discharged with the oil from the discharging port. The rotor is disposed in the operating chamber for its rotation and acting as the pump introducing the oil in the suction passage to the suction port and supplying the oil to the discharged passage via the discharging port. The drive shaft is disposed in the shaft aperture for its rotation so as to rotate the rotor. The sealing member is disposed in a boundary between an outer peripheral surface of the drive shaft and an inner peripheral surface of the shaft aperture so as to seal the boundary. A flow control valve is disposed in the discharged passage so as to return an excess oil to the suction passage in response to operation thereof.
Both ends of the rotor possess a predetermined clearance between adjacent members thereof and are sildaly in contact therewith via oil films. In the aforementioned structure, the oil may leak from the contact surfaces to the drive shaft. The leaked oil is guided to the sealing member from the outer periphery of the drive shaft and is returned to the suction passage via a drain bore defined in the base portion. The drain bore includes a drain inlet communicating with the shaft aperture, a drain outlet communicating with the suction passage, and a drain connecting passage for connecting the drain inlet and the drain outlet. An opening diameter of the drain outlet is designed to be small in light of an inner structure of the oil pump apparatus, an wall thickness of the base portion and the like.
In the above-described oil pump apparatus, while the pump apparatus is running the oil leaked at the outer periphery of the drive shaft is introduced by the drain inlet and drained from the drain outlet to the suction passage maintained at a relatively low pressure level.
Recent developments have led to increasing pressure generated by the oil pump apparatus and increasing an amount of oil discharged therefrom. Especially in accordance with these recent technological developments, the oil may be returned to the suction passage at a relatively large amount in response to the operation of the flow control valve. In this case, the return oil flow speed may become relatively high. This may cause deterioration of oil drain performance for draining the oil from the drain outlet, wherein the space sealed with the sealing member may be unnecessarily applied with a high pressure. Therefore, there may be concern that the seal lip portion of the sealing member may wear out earlier than expected and the sealing member may be dropped off.
There is a need to provide an improved oil pump apparatus capable of assuring the oil drain performance for draining the oil from the drain outlet and capable of reducing the wear-out of the sealing member even if the oil pressure and the oil amount from the oil pump apparatus has been increased.